A series of oligopeptides mimicking portions of the amino acid sequence at the postulated contact regions between neighboring hemoglobin molecules are synthesized. The addition of these compounds such as beta 1-6 hexapeptide amide to concentrated deoxyhemoglobin S solution at various molar ratios raises the minimum gelling concentration (MGC) of hemoglobin S to over 70% when (peptide)/(heme) is larger than two. Shorter peptides such as tripeptide amides are less effective. The specificity of these potential antiaggregation agents or the lack of it is tested by permutating the beta 1-6 sequence or even using other oligopeptides as additives. The results so far seem to suggest that they are equally effective. The recent reports that certain amino acids such as L-homoserine, L-glutamine and L-asparagine, which do not rise the MGC in vitro, can inhibit the sickling and reverse the sickle cell to normal shape have raised the question about the effect of gelation on deformability. Work is in progress to study the relationship, if any, between red cell deformability and hemoglobin S gelation. BIBLIOGRAPHIC REFERENCE: Kubota, S., Chang, C.T., Samejima, T. & Yang, J.T. (1976) Oligopeptides as Potential Antiaggregation Agent for Proteins: Hemoglobin S Gel and Insulin Dimer. J. Amer. Chem. Soc. 98, 2677-2678.